Electron beam tube



March -10, 1 959 F. H. NICOLL ELECTRON BEAM TUBE 2 Sheets-Sheet 1 FiledJune 2. 1955' March 1959 F- H. QNICOLL 25,877,369

ELECTRON BEAM TUBE Filed June 2. 1955 2 Sheets-Sheet 2' wwwi ApplicationJune 2, 1955,. SerialNo. 512,757 10 Claims. (Cl. 313-82l The presentinvention relates generally to an electron beam tube and, though notlimited thereto, is herein described as embodied in a cathode ray tubehaving a multi-apertured electrode for modulating the intensity of theelectron beam therein.

The tube of the invention is characterized by a relatively hightransconductance, a relatively lowmodulation voltage requirement, and arelatively good focus at high beam currents and consequently provesadvantageous in television receivers, especially in such receiversusing-1 transistors in the video amplifiers thereof. 3

Previous cathode ray tubes have ge'nerallyused a control'electrodehaving a singleaperture through which. the beam passed and whichrequired a relatively large negative signal voltage for the whole rangeof beam modulation. Thus, where such tubes areused for image viewingpurposes, e. g. for television, additional amplifier stages have beenrequired to provide the required relatively large negative control'or'signal voltages.

.It is therefore an object of the invention to provide an electron beamtube having an improved electronoptical system for relatively high beamcurrents.

It is a more particular aim to prbvide an improved cathode ray tubehaving a multi-apertured modulating electrode and which exhibits arelatively high transconductance, low cut-off beam modulating voltage,and good beam definition and which is adapted to operate at relativelyhigh beam currents.

The foregoing and related objects are achieved in accordance with theinvention by providing an improved-- electron beam tube havingv acathode and, grid spaced along the tube axis. The grid has"-atleast oneaperture therethrough and has an axial thickness'of between about 5 andabout 60 percent of the minimum distance across at least one aperture.A' multi-apertured diaphragm or mesh is fixed to the side of the gridadjacent to the cathode. Consequently, eachof f the apertures of themesh acts as a separate beam control element for individually focusing aportion of the beam current at a common point within the tube or at aplurality of-points having a predetermined spacing, therebet-ween, thefocus usually being at a target electrode of the tube.

The invention is described in greater detailin connection with theaccompanying two sheets of drawings wherein:

Figure l is a side view, partly in section, of a cathode ray tubeembodying the inventionj I Figure 2 is an enlarged sectional'view of aportion of the tube of Figure 1 and. illustrating'a space potentialdistribution between some of the electrodes of the tube;

Figure 3 is a chart illustrating the'control'grid voltage required tobias one conventional cathode ray tube under various conditions incomparison with. the control grid voltage required to bias one tube ofthe invention under similar conditions;

Figures 4 through 8 illustrate diflerent types of control electrodeswhich may be used in the tube of Figure 1;

a United States Patent 0 v 53 of the grid 30 adjacent to the cathodepins 18: for providing 1C6 Patented Mar. 10, 1.959

Figures 9 through 11 illustrate portions of diflf'erent types ofelectron gun structures useful inthe tube of Figure 1;

Figure 12 illustrates a portion of an electron gun for producing twoelectron beams within a cathode ray tube of the invention; and

Figure 13 shows a control electrode of a type useful in the electron gunof Figure 12.

Reference is made to Figure l where there is shown a side elevationalview, partly in section, of a cathode ray tube 10 according to theinvention and comprising an; evacuated envelope 12 made of an insulatingmaterial, such as glass. portion 14 terminated by a base 16 having aplurality ofelectrical access to some of theelements within the tube 10;the other part of the envelope includes a flared bulb portion 20 closedby a trans-1 parent end-wall 22. The. transparent end-wall carries onthe inside surface thereof a target element in the form of a fluorescentscreen 24, the screen becoming lumines-- cent onbeing bombarded byelectrons.

An electron gun 26 is disposed within the neck portion 14 to provide abeam of electrons directed toward the. gun 26 includes a cathode 28 vhaving a heater therein (not shown),

of tube, are fixed; by being joined to insulating over the inner surfaceof the envelope bulb portion 20- to a point adjacent to the fluorescentscreen 24. This. coating 40 prevents the operation, which would anddeflection.

Means are provided for focusing and scanning the electron beam over thescreen 24 to form a raster. means may include a focusing coil 42 Thesetion 14 adjacent to the flared envelope yoke 44 comprises a plurality ofcoils deflecting fields in the beam path for providing scansion of theelectron beam over the screen 24.

In Figure 2 there is shown the approximate shape of an electron beam(shown in the drawing bounded by lines 46) and an electrostatic field,illustrated by equipotential lines 48, in relation to the cathode 28,control grid 30, and first accelerating electrode 32 of Figure 1. Thecontrol grid 30 has a single, large aperture 51 there'- through in adirection along the tube axis. A multiaperturcd diaphragm or meshelement 50 is disposed across the single aperture 51 and is fixed to theend-wall 28. The mesh element may be in any multi-apertured planar shapeand is fixed to the control grid by any of the known techniques forwelding a mesh element to a support. For example, the welding may beeffected by a hydrogen firing operation while the mesh element ismaintained in contact with the solid portion of the grid by means of ajig. The equipotential field lines 48 adjacent to the aperture 51 aregiven a curvature at the aperture due to the penetration of the fieldinto the end-Wall 53 a substantial thickness. tical field whichpenetrates the small apertures 49 of the mesh element 50 accelerateselectrons at the cathode 28 into a plurality of substantially parallelbeams directed from the surface of the cathode through the small 'aper-'tures 49. Then, while the electrons are still traveling at portion 20.The

One part of the envelope-includes a neck electrodes, which The secondaccelerating electrode" glass portions of the envelope. 20 from becomingindiscriminately charged during tube adversely affect beam focusing anda deflection yoke 44 disposed around the part of the tube neckporforming magnetic:

which has The portion'of the electron-opresolution at relatively arelatively low velocity, that within and just beyond the large aperture51, the portion of the electron-optical field between the grid 30 andthe first accelerating electrode 32 converges the electrons into arestrained region, D, where the beam exhibits a minimum cross-sectionalarea. The focusing coil 42 (Figure l) is then used to image the beamfrom this region (D) at the screen 24.

The curvature of the electron-optical field in the large aperture 51,which produces the minimum cross-sectional area at point D, isdetermined by the spacing between the cathode 28 and the end-wall 53 andby the axial thickness (dimension B) of the end-wall. It has also beenfound that the optimum aforedescribed converging action within the largeaperture 51, when a mesh is used across this aperture, is obtained whenthe thickness of the endwall portion 53, dimension B, is from about 5percent to about 60 percent of the distance, dimension A, across thisaperture.

' In order to obtain a relatively large penetration of theelectron-optical field (Figure 2) through the control grid mesh 50 andadjacent to the active surface of the cathode 28, a relatively closecathode-to-mesh spacing is used. The cathode-to-mesh spacing ispreferably smaller than the distance across an aperture in themulti-apertured mesh 50. For example, one tube made according to theinvention had a distance of about .003 inch across each of the smallapertures in the multi-apertured mesh and a. cathode-to-mesh spacing ofabout .0015 inch during normal tube operation.

It has been found that for a given grid thickness B, a good focus at thescreen or target of the tube can be obtained only for a certain range ofcontrol grid to first accelerating electrode spacings (dimension C inFigure 2). A ratio of the distance represented by the thickness B of thecontrol grid wall to the distance C between the control grid and thefirst accelerating electrode equal to about 1:3 to about 1:10 has beenfound to give satisfactoryresolution at the target. A ratio of fromabout 1:3 to about 1:5, i. e. of the order of 1:4, gives an optimum highbeam currents such as, for example, 300 microamperes. It has also beenfound that the distance between the control grid and the first ac-"celerating electrode should be from about .2 to about one and a halftimes the distance A across the control grid aperture for the bestresolution with the aforementioned: ratios.

For example, cathode ray tubes incorporating electron guns having thefollowing electrode dimensions and spacings have yielded the resultsindicated below. In each case the resolution at the target electrode wasmeasured when the beam current was of the order of 300 microamperes (thebeam being cut-off when the grid volt-r age was lowered to -5 volts withrespect to the cathode), the distance across the large aperture in thegrid being .035 inch and the cathode-mesh spacing with the cathode atthe temperature of normal tube operation) being about .0015 inch.

Control Grid Control Grid- Thickness, First Accnlcr- Resolution B atingElectrode at Target Spacing, C

.005 .010 Poor. .005 .020 Good. .007 032 D0. .009 032 Do.

' and a 60% transmissivity and with crossed wires at the center of thecontrol grid aperture 51. Similarly, Figure 5 shows a wire-mesh 50b ofthe type depicted in Figure4- but with a mesh opening centered in thelarge aperture 51 in the control grid. Figure 6 illustrates yet anotherI mesh element 50c, this one having a spider-web-like mesh.

, minimum distance across the aperture.

element 502 therein (Figure 13).

As shown in Figures 7and 8 the single large aperture 51 in the controlgrid 30 may be square or rectangularly shaped, the dimension A in eachcase referring to the As illustrated in 50d may take the formcf anapertured plate instead of a wire mesh as in the afore; described meshelements. Also, the apertures in the, control grid 30. may take the formof a plurality of apertures and with each of the apertures itself havinga mesh In the last named ar rangement there is provided, in effect, acontrol element having a plurality of apertures wherein each of theaper; tures is itself sub-divided by a mesh element into a plurality ofapertures. In each of the aforementioned ex amples the mesh element isof a multi-apertured, substantially planar shape and is preferablysubstantially symmetrical about the center of the large aperture 51.

Figures 9, 10, vand 11 illustrate portions of different. electron gunassemblies which may be used with a mesh element 50 fixed to a controlgrid. In these three figures.

Figure 8, the mesh element as well as in Figure 1 the mesh element 50 isindicated schematically; it will be appreciated that the mesh element isactually fixedto the grid 30 as shown in Figure 2. While the meshelement 50 may be a flat element (Figure 9) fixed around its peripheryto a fiat control grid 30,

' beam being subject from each other at the control grid surface mayinstead be bowed either out-Q wardly (Figure 10) or inwardly (Figure 11)in order that the mesh follow the contour of the control grid surface towhich the mesh is fixed. The bowing illustrated in Figures 10 and 11(which is exaggerated in the drawing for purposes of illustrating thebowing) is used to' prevent the mesh from buckling when heated, duringnor-iv mal tube operation, and short circuiting to the cathode- 28. Thebowing gives a pro-stressed effect to the mesh forcing it to move, if atall, in the same direction as' that in which the control grid surface isbowed. Thus the distance of the mesh to the cathode is determined 'by',the control grid surface contour. The aforedescribedj bowing is notchosen to be of such a degree that it ap-I preciably affects theelectron-optics (focusing in particu': lar) of the tube in which the gunis used. [1 Reference is made to Figure 12 where there is illus-" trateda portion of an electron gun of a type capable of producing twoseparate, focused electron beams, each to control by a grid-cut-off biasof about --5 volts. The electron gun of Figure 12 has a; control grid 30having two-large apertures 51 and a wire mesh 50 across each of thelarge apertures. While the use of appropriate second acceleratingelectrode to first acf celerating electrode voltage ratios brings thetwo beams to focus at a single point on the screen of the tube, when thesecond accelerating electrode to first acceleration elec-'' trodevoltage ratio is greater than about 50 to 1; the two beams come to twofoci at the screen, and separated by about .075 inchithereat, when thesecond accelerating electrode to.first accelerating electrode voltageratio is between about 10 to l to about 30 to 1. The use of two beamshaving individual foci at a predetermined distance the screen is usefulin eliminating the appearance of a line structure between adjacent scansions on the screensof a television viewing tube.

What is claimed is:

1. An electron beam tube having a tube axis, a cathode and a controlgrid spaced along said axis, said grid having a portion lyingsubstantially in a predetermined surface, said portion having at leastone aperture therethrough and having an axial thickness of between about5 and about 60 percent of the minimum distance across said at least oneaperture, and a multi-apertured mesh fixed to the side of said gridportion adjacent to said cathode and across said at least one apertureand lying substantially parallel to said surface.

2. The electron beam tube described in claim 1 and wherein said controlgrid has two apertures.

3. The electron beam tube described in claim 1 and wherein said at leastone aperture is of substantially circular cross-sections.

4. An electron beam tube comprising a cathode for providing a source ofelectrons, a target, an accelerating electrode intermediate said cathodeand said target for accelerating electrons from said cathode toward saidtarget, and a control electrode intermediate said cathode and saidaccelerating electrode for controlling the flow of electrons toward saidtarget, said control electrode having a portion thereof defining anaperture therein and a multiapertured mesh element across said apertureand fixed to the side of said electrode adjacent to said cathode, thethickness of said control electrode portion being between about 5% andabout 60% of the minimum distance across said aperture, the ratiobetween the distance represented by the thickness of said controlelectrode portion and the distance between adjacent portions of saidelectrode portion and said accelerating electrode being from about 1:3to about 1:10.

5. An electron beam tube comprising a cathode for providing a source ofelectrons, a target, an accelerating electrode intermediate said cathodeand said target for accelerating electrons from said cathode toward saidtarget, and a control electrode intermediate said cathode and saidaccelerating electrode for controlling the fiow of electrons from saidcathode toward said target, said control electrode including anapertured element and a multi-apertured diaphragm across the aperture insaid element and fixed to the side thereof adjacent to said cathode, theratio between the distance represented by the thickness of saidapertured element and the distance between said element and saidaccelerating electrode being from about 1:3 to about 1:10.

6. An electron beam tube comprising a cathode for providing a source ofelectrons, a target, an accelerating electrode intermediate said cathodeand said target for accelerating electrons from said cathode toward saidtarget, and a control electrode intermediate said cathode and saidaccelerating electrode for controlling the flow of electrons from saidcathode toward said target, said control electrode including anapertured element and a multi-apertured diaphragm across the aperture insaid element and fixed to the side thereof adjacent to said cathode,adjacent sides of said diaphragm and said apertured element havingsubstantially the same contour, the ratio between the distancerepresented by the thickness of said apertured element and the distancebetween said element and said accelerating electrode being from about1:3 to about 1:5.

7. An electron beam tube comprising, spaced along a tube axis, a cathodefor providing a source of electrons, a target, an accelerating electrodeintermediate said cathode and said target for accelerating electronsfrom said cathode toward said target, and a control electrodeintermediate said cathode and said accelerating electrode forcontrolling the flow of electrons from said cathode to said target, saidcontrol electrode including an element having a single circular apertureaxially therethrough and a multi-apertured diaphragm across said singleaperture and fixed to the side thereof adjacent to said cathode, thesmallest cross sectional distance across each of the apertures in saiddiaphragm being greater than the distance between adjacent surfaces ofsaid diaphragm and cathode during normal tube operation, the ratiobetween the distance represented by the thickness of said aperturedelement and the distance between said element and said acceleratingelectrode being of the order of 1:4.

8. A cathode-ray tube comprising a cathode for providing a source ofelectrons, a target, an accelerating electrode intermediate said cathodeand said target for accelerating electrons from said cathode toward saidtarget, and a control electrode intermediate said cathode and saidaccelerating electrode for controlling the flow of electrons from saidcathode toward said target, said control electrode including anapertured portion lying substantially in a predetermined surface and amultiapertured diaphragm across the aperture in said portion and lyingsubstantially in said surface and fixed to the side thereof adjacent tosaid cathode, the thickness of said portion being from about .05 toabout .6 of the average distance across the aperture in said element.

9. A cathode-ray tube comprising a cathode for pro viding a source ofelectrons, a target, an accelerating electrode intermediate said cathodeand said target for accelerating electrons from said cathode toward saidtarget, and a control electrode intermediate said cathode and saidaccelerating electrode for controlling the flow of electrons from saidcathode to said target, said control electrode including an elementhaving a circular aperture therein and a multi-apertured diaphragmacross the aperture in said element and fixed to the side thereofadjacent to said cathode, the distance between said element and saidaccelerating electrode being from about .2 to about one and a half timesthe diameter across the aperture in said element.

10. An electron beam tube comprising a cathode for providing a source ofelectrons, a target, an apertured accelerating electrode intermediatesaid cathode and said target for accelerating electrons from saidcathode through said accelerating electrode and toward said target, anda control electrode intermediate said cathode and said acceleratingelectrode for controlling the flow of electrons from said cathode towardsaid target, said control electrode including an element having acircular aperture therein and a multi-apertured wire mesh across theaperture in said element and fixed to the side thereof adjacent to saidcathode, the smallest cross sectional distance across each of theapertures in said mesh being greater than the distance between adjacentsurfaces of said mesh and cathode during normal tube operation, theratio between the distance represented by the thickness of saidapertured element and the distance between said element and saidaccelerating electrode being of the order of 1:4, the thickness of saiddisc being from about .05 to about .6 of the diameter of the aperture insaid element, and the distance between said element and saidaccelerating electrode being from about .2 to about one and a half timesthe diameter of said aperture in said element.

References Cited in the file of this patent UNITED STATES PATENTS2,153,223 Young Apr. 4, 1939 2,299,047 Winans Oct. 13, 1942 2,644,906Bondley July 7, 1953 2,726,347 Benway Dec. 6, 1955

